Coating apparatus

ABSTRACT

Coating apparatus suitable for depositing superimposed layers of two different viscous liquids or pastes on a support is provided which comprises a pair of hoppers having one lip common to both hoppers, forming the downstream lip of the upstream hopper and the upstream lip of the downstream hopper.

United States Patent Hathorn 1 Feb. 15, 1972 541 COATING APPARATUS [56]References cam [72] Inventor: George Stuart Hathorn, Dagenham, Dock,UNITED STATES PATENTS En and g! 1,957,611 5/1934. Pelton.. ..118/415 X 1u Porvalr u Dagenham. Dock, 1311- 2,932,855 4/1960 Bartlett et a].18/412 x gland 3,206,323 9/1965 Mi1ler etal ..1 18/411 X [22] Wed: 1969Primary Examiner-John P. McIntosh [21] App1.No.: 789,570 Anomey-Watson,Cole, Grindle&watson [30] Foreign Application Priority Data [57] ABS CT1 Coating apparatus suitable for depositing superimposed layers Jan. 9,GreatBntam of two difi-erent viscous orlpastes on a pp is p v videdwhich comprises a pair of hoppers having one lip com- 52] us. c1..1l8/412,118/413,118/415, men to both hoppers forming the downstream upof the up 118/428 stream hopper and the upstream lip of the downstream[51] Int. Cl. ..B05c 3/18, B050 3/12 hoppen A j [58] fieldofSearch..1l8/4l2,411,413,415,428

1 Claims, 2 Drawing Figures PAIENTEUFEB 15 I972 SHEET 1 OF 2 INVENTORGun SfKnmm BY ATTORNEY PATENTEDFEB 15 1912 SHEET '2 [IF 2 INVENTOR IGEDRGE S. KKYR QN,

/ ATTORNEY The present invention relates to coating apparatus for makingsheet material which, for one reason or another, is made in two or moresuperimposed layers. Such a material can conveniently be made by aprocess which includes the step of coating the working ingredients whilein a viscous liquid or pasty state on a support.

According to the present invention, coating apparatus suitable fordepositing superimposed layers of two different viscous liquids orpastes on a support comprises a pair of hoppers respectively adapted tocontain coating material and each having anarrow outlet slot beneathwhich a support is arranged to be passed to deposit a layer of theassociated material, each outlet slot being bounded by upstream anddownstream lips whereof each downstream lip forms a doctor blade todetermine and smooth the upper surface of the associated .material, inwhich one lip is common to both hoppers, forming the downstream lip ofthe upstream hopper and the upstream lip of the downstream hopper. Eachdownstream lip may be adjustable so as to provide a variable outlet slotwidth.

The material used for one layer may be of a higher viscosity than thatused for a succeeding layer, but the apparatus can be used even whenthis requirement is not fulfilled.

The apparatus in accordance with the present invention reduces thedanger of air being entrapped between the layers with consequentreduction in the strength of bonding between the layers. It alsoprevents the downstream paste or liquid from leaking beneath its doctorblade.

There are various reasons for making a layered material such as thepresent one. For example, natural leather comprises a main fiber layerand a surface layer termed the grain layer, and in making an artificialleather it is often thought desirable to provide two layers havingrather different properties to simulate these two layers of naturalleather. In other cases the purpose of the exposed layer may be merelyto give a pleasing appearance or a desired color while employing for thegreater part of the thickness a material having other desirablequalities such as strength or toughness, or cheapness. Again it may bedesirable that the exposed layer should be waterproof while the otherlayer may have a degree of water absorbency.

The difficulty has arisen in process for making layered microporousmaterials in which the working ingredients for one layer are applied toan already formed lower layer that the solvent employed in the formerpartly dissolves the surface of the latter and adversely afi'ects itsstructure, for example, by collapsing its micropores. To overcome thisdifficulty ithas been proposed to interpose a tie layer between the twolayers, the solvent for each layer being chosen so as not to dissolve oradversely affect the preceding layer. Naturally this adds considerablyto the complexity of the method.

It has been found that if the mixture from which the upper layer isformed is deposited on the lower layer mixture before the latter iscoagulated or solidified, the two layers-can be coagulated at the sametime and the difficulties referred to above do not arise. This forms thesubject of the commonly owned US. Pat. application Ser. No. 697,165, 165filed Jan. 1 l, 1968, which relates to a process of making a layered andporous water vapor permeable flexible sheet material, and the presentinvention is particularly, through not exclusively applicable to theprocess described in that specification.

The hopper outlets may be arranged around a roll and the support, whichmay be of strip form, and may be passed around the roll so as to besupported by the roll as it passes beneath the hoppers.

The hoppers can be fed with the coating material under pressure and thusneed not be located at the top of the roll. However, it is convenientfor the coating material to be discharged under gravity since issimplifies the apparatus. It is thus preferable to locate the hoppers atthe top of the roll.

One embodiment of the invention, in which the apparatus is used to coattwo different pastes on to a strip of support material, will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevation of the coating apparatus; and

FIG. 2 is a diagrammatic plan view of the coating apparatus.

in this embodiment, the apparatus is used to coat two different pastesof polymeric plastics material, a substrate paste and a less viscous topcoat paste, on to a flexible strip of support material through asmentioned above. the apparatus is also suitable for coating materialshaving a difi'erent relationship between their viscosities. The supportmaterial, which in this case is a strip of porous polyethylene sheetmaterial, is mounted as a roll 1 on a braked wind-off stand 2 from whichit passes as at 3 around a ground steel spreading roll 4, and then, byway of guide rolls 5 and guideway strips 6 to further processing stagesincluding a dunk tank 25 where the spread pastes are coagulated byimmersion in a treatment liquid and thereby solidified to formsuperimposed solid layers. Guideway strips 6, a single pair of which areonly shown in FIG. 1, are mounted along the inner sidewalls of tank 25at opposite sides of the support material.

Located just above the spreading roll, in the vicinity of its verticalcenterline, is the coating apparatus. This comprises, in order (fromleft to right in FIG. 1) a downstream doctor blade 10, an upstreamdoctor blade 11 and an upstream backing plate 12, all three componentsbeing arranged in planes containing a line parallel to the axis of thespreading roll 4. The lower edge of the backing plate 12 is held againstthe support 3 as it moves around the spreading roll 4, while the loweredges of the doctor blades 10 and 11 are held a short but adjustabledistance above it, that of the upstream blade 11 being the closer to thesupport 3. Cheekpieces l3, l4, l5 and 16 are held across the spacesbetween the blades 10 and 11 and the backing plate 12 to define a pairof hoppers l7 and 18, the former between the backing plate 12 and theupstream blade 11, and the latter between the doctor blade 10 and thedoctor blade 11 (which forms a backing plate for the hopper 18).

The doctor blades 10 and 11 have chamfered trailing edges 20 and 21respectively, and flat bases, in an alternative arrangement, it is theleading edges of the blades that are chamfered.

precise location with respect to the spreading roll, depends to someextent on the nature of the two pastes, by a typical arrangement is asfollows:

Diameter of spreading roll 4: 18 inches.

Gap setting of doctor blade 10 from the support 3: 0.125

inches.

Gap setting of doctor blade 11 from the support 3: 0.100

inches.

The doctor blade 11 is parallel to the vertical center line of thespreading roll 4, but somewhat to its right as viewed in FIG. 1. Thedoctor blade 10 and the backing plate 12 are arranged on either side ofthe doctor blade 11, sloping away from it at angles of 35 and 39respectively, the three components lying in planes which intersect in aline parallel to the axis of the roll 4 and displaced from ithorizontally.

A supply of topcoat paste is placed in the hopper l8 and a supply ofsubstrate paste in the hopper 17. The doctor blades 10 and 11 areadjusted to provide appropriate gaps between their lower edges and thesurface of the support 3.

Thus, as the support 3 is fed from its braked wind off roll around thespreading roll 4, a layer of substrate paste is spread on its surface bythe upstream doctor blade 11, and then, in close succession, a layer oftopcoat paste is spread on the layer of substrate paste by thedownstream doctor blade 10.

The arrangement described gives a substrate wet coating thickness of theorder of 0.09 inches for a substrate paste of viscosity of the order of200,000:l0,000 centipoise, and a topcoat wet coating thickness of theorder of 0.05 inches for a topcoat paste of viscosity of the order of100,000il 0,000 centipoise, the viscosities being measured at 25 C.viscosities were measured on a Brookfield R.V.T. viscometer using a No.7 Spindle at 10 r.p.m.

The detailed geometry of the coating apparatus, and its The apparatushas been used to produce coatings up to 3 mm. thick and has been usedwith pastes having viscosities of the order of 25,000 centipoise to2,000,000 centipoise.

Further details of the method and apparatus are described in theabove-mentioned US. Pat. application Ser. No. 697,165.

What we claim as our invention and desire to secure by Letters Patentis:

l. Coating apparatus comprising a support of strip form, a roller, apair of hoppers, the support being arranged to pass around said rollerand be supported by said rollers as it passes beneath said hoppers, tankmeans adapted to contain liquid, and guide means, whereby said supportmay be passed from said roller through said tank means beneath thesurface of the liquid in said tank, when the apparatus is in use, withsaid support uppermost under the guidance of said guide means, said pairof hoppers respectively being adapted to contain coating material andeach of said pair of hoppers having a narrow outlet slot beneath whichsaid support is arranged to be passed to deposit a layer of theassociated material, each said outlet slot downstream lip of saidupstream hopper and the upstream lip of the downstream hopper, and saidhopper outlets being arranged around the periphery of said roller.

l l il

1. Coating apparatus comprising a support of strip form, a roller, apair of hoppers, the support being arranged to pass around said rollerand be supported by said rollers as it passes beneath said hoppers, tankmeans adapted to contain liquid, and guide means, whereby said supportmay be passed from said roller through said tank means beneath thesurface of the liquid in said tank, when the apparatus is in use, withsaid support uppermost under the guidance of said guide means, said pairof hoppers respectively being adapted to contain coating material andeach of said pair of hoppers having a narrow outlet slot beneath whichsaid support is arranged to be passed to deposit a layer of theassociated material, each said outlet slot being bounded by upstream anddownstream lips wherein each said downstream lip forms a doctor blade todetermine and smooth the upper surface of the associated materialindependently through each said outlet slot, one of said lips beingcommon to both said hoppers thereby forming the downstream lip of saidupstream hopper and the upstream lip of the downstream hopper, and saidhopper outlets being arranged around the periphery of said roller.